1. Field
The invention relates to electrical engineering, in particular, to automated emergency devices for electrical substations and switchgears of low, medium and high voltage, and can be used for detecting failures of power supply to consumers from a primary power source due to any faults in the power circuit of a switchgear section, and for quick switching to a backup power source.
2. Description of the Related Art
A known method for automatic activation of a backup power supply to consumers (USSR Inventor's Certificate No. 1728927, H 02 J 9/06, 1990) is embodied by measuring a positive-phase-sequence voltage at busbars in a primary and a backup power sources and by measuring an angle between vectors of the positive-phase-sequence voltages at busbars in the primary and the backup power sources. The direction of active power flow at input of the primary power source busbars is then determined. The busbars of the primary source are switched to the backup source if the positive-phase-sequence voltage in the primary power source is below a set value or if the angle between the vectors of the positive-phase-sequence voltages exceeds a value, and when the active power flow is directed from the busbars to the primary power source. The direction and value of a reactive component of the positive-phase-sequence current at input of the primary source busbars, value of the negative-phase-sequence voltage at the busbars in the primary source are determined. When directing the positive-phase-sequence reactive current component from the busbars to the primary source, if said reactive component and the negative-phase-sequence voltage of the busbars in the primary source exceed the values, the busbars are switched from the primary source to the backup source, Field forcing of synchronous motors is performed in all cases simultaneously with the switching procedure.
Unfavorably, the above method does not provide determination of single-phase, double-phase and double-phase line-to-ground short circuits in power circuits for supply to consumers due to the fact that direction of active power at the input of substation in these modes remains unchanged, and the active power is still used by connected consumers. In case of any short circuits in the power circuits, direction of the reactive component of the positive-phase-sequence voltage remains unchanged if no motor load is applied to the switchgear section.